This invention relates to the preservation of fresh produce, and more specifically to methods and apparatus for packaging perishable fruits such as strawberries. The invention preserves and protects fresh fruit during storage and shipment from the cooling facility to the distant marketplaces through the world.
Strawberries are picked in the fields and placed into a small plastic container, some of which have foldable lids, while others are open faced. These containers typically are about 4".times.4" or 5".times.7". The plurality of the packed containers are placed into open faced cartons which are stacked onto a pallet for transportation of the containers of fresh produce.
The produce is brought from the field to a cooling facility where the entire pallet of strawberries is brought down to a temperature no less than about 33 degrees Fahrenheit and no more than about 40 degrees Fahrenheit, preferably 34 degrees F.
Often for distant markets, the stacks of cartons is wrapped in some form of flexible material. Typically, this flexible packing material is sealed around the stack of cartons. In a presently used system, the interior of the package is exhausted with a vacuum, and recharged with carbon dioxide gas. A variety of packaging methods and equipment are reported. In another reported system the interior of the package is flushed with a gas under pressure, such as a nitrogen rich gas, or may be exhausted with a vacuum. If a vacuum has been used, the interior typically may be charged with carbon monoxide, carbon dioxide, oxygen and mixtures thereof.
There are many disadvantages to the system that is currently in use. Number one, the systems used today are inefficient. Secondly, carbon dioxide gas is not the ideal gas to be used for this process. Last of all, the packaging film used does not perform as needed for quality assurance.
First, the systems used are not economically nor ergonomically efficient. With most systems, there is a designated room or wide area within the cooling facility to operate the large, stationary machine used in the process. This is valuable, cooled space that could be used for holding/storing produce awaiting transit. Next, the process of packaging the stack of cartons involves an excessive amount of labor, time, and equipment. After the stack of cartons has been covered, an operator must transport the package from a holding room to the designated area with a forklift. Another operator, then seals, exhausts, and recharges the package with the machine. After which, the package is picked up again with the forklift and taken back to the holding facility or loaded onto a waiting truck. The entire system and process can be made much more efficient by implementing a much smaller machine that is portable throughout the cooling facility, and eliminating the steps of moving the package to another room for the gas process and returning the package to the holding room.
Secondly, carbon dioxide is not necessarily the "ideal gas" for preserving strawberries. CO2 gas alters the taste of the fruit and is too permeable to the package that holds it. The process that is used today exhausts the package of oxygen and replenishes it with carbon dioxide as a preservative gas. When fruit is starved of oxygen it begins to ferment, giving off acetaldehyde, ethanol, and ethyl acetate, in turn altering the taste. CO2 is also 16/1 times more permeable to polyethylene film than nitrogen, meaning that when placed into the package, the gas quickly escapes. In a short time, excessive CO2 can absorb into the fruit creating a "fizzy" taste in the strawberry, different from the fermented taste. Also, when CO2 is injected into the stack of cartons it leaves an oil residue on the produce, which affects the skin of the fruit and again the taste. CO2 does preserve the fruit from gray mold, a bacteria that feeds on oxygen, but in the process of which it is used, it alters the fruit's taste before it reaches the consumer in the marketplace.
Next, there are problems with the flexible material that is used. The material presently used is too thin to provide an insulation barrier significant enough to protect the perishable fruit from exposure to the elements, such as fluctuating temperatures while loading or unloading or within the transport trailer, and wind chill caused by refrigeration units. The material is also not strong enough to endure chafing amongst packages causing the seal of the package to fail. Finally, the low density polyethylene film (LDPE) is not as effective as other materials available, in controlling the permeability of the gases within the package to those which are in the atmosphere.
Some more sophisticated systems regularly or continuously measure one or more characteristics of the gas, and change the gas content to maintain a desired gas condition. Such systems are used on large sea containers and air cargo containers. The expense of the metering devices needed make these systems unsatisfactory for produce moving from the field to the retail store in this country.
Accordingly, it is an object of the present invention to provide a new and improved method and apparatus for overcoming these disadvantages.
Other objects, advantages, features and results will more fully appear in the course of the following description.